As we know, the H.265 codec is only used by Apple in FaceTime on its iPhone 6 and latter models. So users can't stream or play H.265-encoded video outside of the FaceTime enviroment. Therefore, it does not work when you tried playing H.265 video on QuickTime player.

To solve H.265 video playback problem on Mac, you can use Pavtube Video Converter for Mac to decode H.265 to QuickTime MOV format, the native file format for QuickTime player. The program also enables you to convert H.265 video to other QuickTime supported file formats such as ASF, DivX Media Format, Flash Video, Matroska, Ogg, etc.

The fact is that currently, you can only use VLC to play H.265 on Mac. For those people who insist on playing H.265 files with QuickTime player, the best solution is transcoding H.265 to QuickTime Player readable file formats such as AVI, DV Stream, MPEG-2, MPEG-4, QuickTime Movie, etc.